Eterno was a villain from The Secret Saturdays. His first and only appearance was in Eterno. He was voiced by Fred Tatasciore.
Eterno was once a warrior king whose thirst for power could not be quenched. So he sought The Methuselah Tree, the tree that makes all the water on earth. He failed, instead being entombed in salt by the tree's protectors, who caused an earthquake. As time passed, he became pure salt; only being woken when touched by water. After his reawakening, he started to turn the oceans into salt. Touching anything with his right hand will turn objects into to salt or entomb them in a layer of salt; his left hand appears to have no effect. Only the Methuselah Tree's sap is immune to his touch.
Eterno's previous lust for power had become a literal thirst, driving him to search for water to drink, but unable to as his salty skin absorbs it. The tree sap, being impervious to him, is also proven to be the thing that can cure him. So he kidnaps Zak Saturday's family to manipulate Zak into obtaining the sap for him, trapping his victims in salt. After being given a flower from the Methuselah Tree, Eterno drinks the sap, letting out a satisfied "ah" as his body crumbles into a pile of salt, his thirst finally quenched.